Mattel confirmed at Comic-Con that the TRU 2-pack with Nightwing is coming later, and the blue Robin set is simply a variant in "Nightwing-like" colors and does not replace it.

All the speculation about the blue Robin replacing Nightwing was just that. It was based on the fact that blue Robin was found but Nightwing was not. Apparently no one thought about th epossibility that the Nightwing set would be released later in the year.